Aggression is a nearly universal feature of the behavior of social animals. In the wild, it is regularly used for access to food and shelter, for protection from predation and for selection of mates. Despite its importance, little is known of the neural mechanisms that underlie the behavior. In almost all species of animals in which it has been looked for, aggression and/or territorial behavior has been found. It is not surprising, therefore, to find that fruit flies also show aggression and territorial behavior. The existence of these behaviors in Drosophila species is not widely known, however, with the exception of the difficult to study Hawaiian species. With powerful genetic and molecular methods available to explore fundamental biological processes, Drosophila melanogaster offers unique opportunities for studies aimed at understanding how a complex behavior like aggression is assembled and activated within, and impacts upon the nervous system. The goals of these studies are to perform a quantitative analysis of fighting behavior in Drosophila melanogaster and to use the analysis to examine the consequences of specific chemical ablations and neuronal mutations on the behavior. There are two Specific Aims of these studies. In the First Aim we plan to: (1) establish conditions under which fighting is a robust phenomenon; (2) use these experimental conditions to videotape and analyze fights in order to construct an ethogram; (3) attempt to define a simplified scoring procedure for fly fights; (4) ask whether there is a long-term component to winning and losing fights in flies. In the Second Aim we plan to: (1) change the levels of amines like serotonin, octopamine and dopamine using chemical and mutant approaches and observe the effects on fighting behavior; (2) examine the fighting behavior of various learning mutants in flies; and (3) abolish mushroom bodies in the brains of flies, which are known to be important in learning and memory, using chemical and transgenic approaches and ask whether decision making ability or the short- and long-term consequences of winning or losing fights are altered. The human health issues these studies relate to are violence, aggression, drug abuse and mental health.